As this type of ball end mill, for example, Japanese Patent No. 3957230 proposes a ball end mill in which a rake angle in a cross-section from the center of the cutting edge in a radial direction is a negative angle at a portion closer to an outer peripheral cutting edge than a position where the cutting edge (radial cutting edge) protrudes farthest forward in a rotation direction from a segment connecting an outer peripheral cutting edge with an axis of a tool, and the rake angle is in the range of 0° to +10° at a portion close to the axis of the tool from the position in a view showing an end face of the tool.
Japanese Patent No. 3957230 discloses as follows: In this ball end mill, a portion where the cutting edge protrudes most from the segment is generally close to a portion where the depth of a groove of the outer peripheral cutting edge is largest and chips are easily removed. Accordingly, it is possible to increase the strength of the cutting edge by setting a rake angle to a negative angle on the outer peripheral side of this portion. Since the strength of the cutting edge needs to be maintained on the side (tool axis side) that is closer to a front end than the portion where the cutting edge protrudes most, the depth of the groove is made small. Accordingly, it is possible to secure the groove by setting the rake angle of the cutting edge to a range of 0° to +10°, which is larger than a negative angle, and to reduce the wear of a tool, which is caused by the generation of an unnecessary force or heat, by making the removal of chips convenient.